Electrodeposition of platinum/iridium (pt/ir) on pt microelectrodes with improved charge injection properties

ABSTRACT

Aspects of the present disclosure are directed to electrochemical approaches for synthesis of platinum-iridium alloys with selected platinum-iridium ratio content and subsequently predetermined mechanical properties and electrochemical impedance properties. Such can provide a simple and cost-effective process for preparing these electrodes, as compared to conventional thin film processing techniques. A three-electrode electrochemical electrodeposition system is described including an electrochemical cell with a working electrode on which the electrodeposited film is deposited, a counter electrode to complete the electrochemical circuit and a reference electrode to measure and control surface potential. Mixed layers of platinum atoms and iridium atoms can be deposited from electrolyte solution onto the working electrode surface to create an electrically conductive surface with material properties related to the composition of the as-deposited film. The mechanical properties and electrochemical properties of the film can be tuned by adjusting the electrodeposition parameters.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 61/237,619, filed 27 Aug. 2009 and entitled“Electrodeposition of Platinum/Iridium (Pt/Ir) on Pt Microelectrodeswith Improved Charge Injection Properties,” the entire content of whichis incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with government support under Contract No.EEC0310723 awarded by the National Science Foundation. The governmenthas certain rights in the invention.

BACKGROUND

Small-scale microelectrodes are used in a number of applications. Onepromising field of application of microelectrodes is for neuralprosthetic medical devices, which are typically used to stimulate nervecells to overcome pre-existing medical conditions. Examples of suchmedical conditions include diseases producing damage to the retina suchas uveitis, retinitis pigmentosa, macular degeneration, diabeticretinopathy and glaucoma. Metallic microelectrodes have been used forneural prosthetic medical devices. Platinum and platinum-based alloyshave proven useful for such microelectrodes because of the high degreeof bio-compatibility afforded.

Platinum and iridium, and the platinum group metals in general, possessthe unique qualities of having multiple oxidation states, conductingoxides, low electrochemical impedance, and enhanced biocompatibility inelectrical stimulating and sensing applications over other conductingmetal materials. These qualities position both platinum and iridium asprime choices for electrode composition in applications such as fuelcell electrodes, hydrolysis reactions electrodes, and implantableelectrodes for sensing and stimulating. Individually, platinum andiridium possess different mechanical properties. Platinum is known to beductile and malleable, while iridium is known to be stiff and brittle.The two are often alloyed to create alloys with improved mechanicalproperties over the individual constituents. The exact ratio of the twois adjusted so as to match the mechanical property requirements for theparticular application, e.g. more platinum where a more ductileelectrode is preferred and more iridium were stiffness is desired. Acommon quality of both materials is high melting temperature, platinum(1772° C.) and iridium (2410° C.). This makes processing and handling ofboth metals a challenge, particularly in the manufacturing of smallcomponents. A variety of thin film processing techniques have been usedto create components and features of this size, e.g., electron beamevaporation and magnetron sputtering in concert with photolithographyand other semi-conductor processing techniques; however, these processesare performed under high-vacuum which is not time-efficient orcost-effective. Additionally, these are thin film coating processes thatcoat series of mono-atomic layers of metal throughout the depositionchamber thus being source-material inefficient.

Another quality of both metals worth noting is their low electrochemicalimpedance. This is attributable to the multiple oxidation states of bothelements, as well as, the electrical conductivity of their oxides thatallow for easier electron transfer between the metal and a surroundingelectrolyte solution. Iridium possesses more oxidation states and itsoxide possesses a lower electrical resistance therefore it shows lowerelectrochemical impedance over platinum and platinum oxide.

Some previous techniques for electroplating platinum and/or platinumiridium have been reported. Such techniques, however, have typicallyutilized corrosive and/or toxic solutions. Moreover, such techniqueshave produced microelectrodes having less than ideal mechanicalproperties and/or electrical properties.

SUMMARY

Aspects of the present disclosure can provide for efficient techniquefor electrodepositing platinum-iridium (Pt—Ir) alloy electrodes. Pt—Iralloy microelectrodes according to the present disclosure candemonstrate improved mechanical properties, e.g., plating adhesion,modulus of elasticity, shear modulus, fatigue strength, etc., andenhanced charge injection properties over standard platinum electrodes.

An aspect of the present disclosure is directed to a method ofdepositing a platinum-iridium alloy or desired mixture of platinum andiridium atoms/molecules onto a base, e.g., a gold of platinum foil orwire. The method can include causing contact (e.g., immersion) between ametal base and an electrolyte solution for electrodeposition, with theelectrolyte solution being biosafe or non-cytotoxic and includingplatinum and iridium. Two or more electrodes can be caused to come intocontact with or presented to or placed in the electrolyte solution. Theelectrodes can be configured to apply an electric potential to orthrough the electrolyte solution. At least one of the two or moreelectrodes can be caused to come into electrical contact with the metalbase. An electric potential can be applied to or across the electrodesin the electrolyte solution in an amount or to a degree sufficient causedeposition of Pt—Ir on the metal base. The deposition can be controlledto produce a desired composition ratio of Pt to Ir.

A further aspect of the present disclosure is directed to a Pt/Irmicroelectrode. The microelectrode can include a metal base of aselected metal composition, and a Pt/Ir film disposed on the metal base.The Pt/Ir film has a desired composition ratio of Pt to Ir. In exemplaryembodiments, the microelectrode can be cylindrical with a desired lengthand a diameter of between about 0.5 micron to about 200 micron (or anydiameter within the range, inclusive of the end values). Other diametersof such microelectrodes (which may be any practical shape) may of coursebe realized within the scope of the present disclosure.

These, as well as other components, steps, features, benefits, andadvantages of the present disclosure, will now become clear from areview of the following detailed description of illustrativeembodiments, the accompanying drawings, and the claims.

BRIEF DESCRIPTION OF DRAWINGS

The drawings disclose illustrative embodiments. They do not set forthall embodiments. Other embodiments may be used in addition or instead.Details that may be apparent or unnecessary may be omitted to save spaceor for more effective illustration. Conversely, some embodiments may bepracticed without all of the details that are disclosed. When the samenumeral appears in different drawings, it refers to the same or likecomponents or steps.

Aspects of the disclosure may be more fully understood from thefollowing description when read together with the accompanying drawings,which are to be regarded as illustrative in nature, and not as limiting.The drawings are not necessarily to scale, emphasis instead being placedon the principles of the disclosure. In the drawings:

FIG. 1 depicts a three-electrode electrochemical cell made of Teflon, asused for exemplary embodiments of the present disclosure;

FIG. 2 depicts a set of cyclic voltammograms achieved duringelectrodepostion of Pt—Ir films, in accordance with exemplaryembodiments of the present disclosure;

FIG. 3 depicts two plots of maximum currents as a function of number ofcycles, for anodic currents (a) and cathodic currents (b), in accordancewith exemplary embodiments of the present disclosure;

FIG. 4. depicts two plots of coating properties vs. deposition time,mass vs. deposition time (a) and coating thickness vs. deposition time(b), in accordance with exemplary embodiments of the present disclosure;

FIG. 5 depicts a set of SEM micrographs, in accordance with exemplaryembodiments of the present disclosure; an Au substrate is shown in (a)and Pt—Ir films are shown in (b)-(e) with 4, 8, 16 and 32 minutes ofdeposition times, respectively;

FIG. 6 depicts a set of cyclic voltammograms of an Au substrate (a),control samples (b)-(d) and Pt—Ir films (e)-(h) with differentdeposition times measured in 0.05 M H₂SO₄, in accordance with exemplaryembodiments of the present disclosure;

FIG. 7 depicts a set of Bode plots for Au substrate, Pt, Ir, 80-20 Pt—Irfoils, and Pt—Ir films in measured in 0.05 M H₂SO₄, in accordance withexemplary embodiments of the present disclosure;

FIG. 8 depicts an equivalent circuit to the electrochemical cell of FIG.1;

FIG. 9 depicts Bode plots of experimental (dots) and fit data (solidline) of Pt—Ir film electroplated for 32 minutes, in accordance withexemplary embodiments of the present disclosure;

FIG. 10 depicts capacitance (a) and 1/Rp (b) values vs. deposition timefor electrodeposited Pt—Ir films, in accordance with exemplaryembodiments of the present disclosure;

FIG. 11 depicts an electrochemical potential scale showing equilibriumpotentials for Pt salts and Ir salts, in accordance with exemplaryembodiments of the present disclosure.

While certain embodiments are depicted in the drawings, one skilled inthe art will appreciate that the embodiments depicted are illustrativeand that variations of those shown, as well as other embodimentsdescribed herein, may be envisioned and practiced within the scope ofthe present disclosure.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Illustrative embodiments are now discussed. Other embodiments may beused in addition or instead. Details that may be apparent or unnecessarymay be omitted to save space or for a more effective presentation.Conversely, some embodiments may be practiced without all of the detailsthat are disclosed.

Aspects of the present disclosure provide for Pt—Ir electrodes ordesired composition and also related fabrication methods withelectrodeposition utilizing novel plating electrolyte solutions and/orusing unique deposition methods. The deposition processes can becontrolled in such a way as to produce Pt—Ir thin films with desiredcomposition and microstructure. For example, embodiments of the presentdisclosure can provide programs for producing thin films of 90% Pt-10%Ir, 95%-5% Pt—Ir, 60%-40% Pt—Ir, etc. Thus, control techniques areprovided for deposition conditions to control Pt—Ir conditions topredictably produce a thin film electrode with predetermined compositionand properties.

Potentiodynamic deposition (deposition using non-steady-state control ofthe potential) can be used for exemplary embodiments of the presentdisclosure. For example, a varying, non-steady-state potential, e.g.,subject to cycling, cyclic potential stepping, and/or triangular-wave(ramp) cycling (within a maximum and minimum potential limit), can alsobe used to deposit metal. These cyclic or non-steady-state approachesdeposit metal for a fixed portion of the cycle, then change thepotential to allow byproducts of the deposition reaction to leave theactive, deposition surface and provide time for new metal reactant tomigrate to the deposition surface or to allow preferential deposition ofone of the two species.

Generally, deposition can, and preferably does, employ a potentialcycling, e.g., a sweeping, stepping, and/or pulsing process, whichdrives the surface potential of the working electrode over a potentialrange that is negative to the equilibrium potential for reduction ofboth the Pt cation salt and the Ir cation salt for at least a portion ofthe potential range. The positive limit of the potential range may bemore positive than both or only one limit, e.g., as described below forFIG. 11. Additionally, the rate at which the potential is swept may beadjusted (either using slow or fast rate) to produce thin films withless internal stress. The deposition may be performed under inert gas ornon-oxidizing gas (N₂) in order to avoid cation oxidation prior todeposition. In some solution chemistries is may be possible to use apotentiostatic deposition program, where the applied potential is morenegative than the equilibrium potential of both the Pt and the Ir salts.

Electrodeposition according to the present disclosure can allow for amore time and cost efficient approach to metal deposition over standardmetal processing techniques, e.g., casting, forging, sputtering,evaporation, etc.

Aspects and embodiments of the present disclosure broadly relate to thecreation of electrodeposited thin films containing platinum and iridiumhaving low-impedance, and more particularly describes a method forcreating such thin films through a process that allows control of: (1)platinum and iridium content; (2) mechanical properties; and, (3)electrochemical impedance properties. More specifically, the inventiondescribes the composition of electrolyte solution and electrodepositionvariables that can be employed so as to predictably produce thin filmelectrodes of known and desirable composition, mechanical properties andelectrochemical properties. As mentioned above, a Pt—Ir plating solutioncan be prepared for the deposition of Pt—Ir films of a desiredcomposition ratio. Exemplary embodiments of the present disclosure canuse plating solutions according to the following methods to achievebiocompatibility; other Pt—Ir solutions can of course be used within thescope of the present disclosure.

In exemplary biocompatible embodiments of the present disclosure, Pt/Irfilms can be electrodeposited from Pt—Ir solution using 0.2 g/L ofSodium hexachloroiridate (III) hydrate, (Na₃IrCl₆·xH₂O) and 0.186 g/LSodium hexachloroplatinate (IV) hexahydrate (Na₂PtCl₆·6H₂O) in 0.1 Mnitric acid (HNO₃). Exemplary embodiments of such solutions were tested,as described below. A plating solution can be boiled and then cooled toroom temperature. Before electrodeposition, the Pt—Ir solutions can bepre-heated, e.g., to 62 C. The solutions can be agitated using anultrasonic homogenizer, e.g., a homogenizer (Misonix, Inc.) at afrequency of 20 kHz with a power of 5 W to maintain constant masstransfer during electrodeposition. The solution(s) can be kept at aconstant temperature constant for such. Preparation of solutions may beperformed under inert gas or non-oxidizing gas (N₂) in order to avoidcation oxidation prior to deposition.

Aspects of the present disclosure are directed to electrochemicalapproaches for synthesis of platinum-iridium alloys with pre-determined,or selected, platinum-iridium ratio content and subsequentlypredetermined mechanical properties and electrochemical impedanceproperties. Such can provide a simple and cost-effective process forpreparing these electrodes, as compared to conventional thin filmprocessing techniques.

In a three-electrode electrochemical system comprising anelectrochemical cell with a working electrode on which theelectrodeposited film is deposited, a counter electrode to complete theelectrochemical circuit and a reference electrode to measure and controlsurface potential, mixed layers of platinum atoms, iridium atoms, andoxides and chlorides of both, are deposited from electrolyte solutiononto the working electrode surface to create an electrically conductivesurface with material properties related to the composition of theas-deposited film. The mechanical properties and electrochemicalproperties of the film can be tuned by adjusting the electrodepositionparameters so as to control the composition and structure of the film.

In applications where a low-impedance electrochemical electrode isrequired for passage of current in the positive or negative directionacross the interface, this method would allow for the electrodeimpedance and mechanical properties to be tailored to meet the designrequirements. Impedance can be controlled by controlling the depositedfilm's surface area and/or platinum-iridium composition ratio.Similarly, where mechanical properties are important, theelectrodeposited film can be deposited with more platinum content inapplications where more ductile properties are desirable, and with moreiridium content when more stiffness and rigidity are required.

FIG. 1 depicts a three-electrode electrochemical system 100 including anelectrochemical cell 102 useful for electrodeposition, in accordancewith exemplary embodiments of the present disclosure. System 100 caninclude a working electrode (WE) 104, reference electrode (RE) 106, andcounter electrode (CE) 108. System 100 can be connected to apotentiostat 110, e.g., a computer controlled potentiostat. Theelectrochemical cell 102 can include a larger diameter electrolytecolumn (A) and a smaller diameter electrolyte column (B), each connectedto one another, e.g., at the cell base via a cross-drilled Luggincapillary (C). A Luggin capillary can facilitate creation of awell-defined short electrolytic path between the working electrode (WE)104 and the reference electrode (RE) 106. The working electrode (WE) 104can include (or be used with) a conductive layer or plate for electricalconnection to electrolytic solution in cell 102, e.g., a conductiveplate 120, as shown. A gasket or sealing structure, e.g., a polymero-ring, can be placed between cell 102 and conductive plate 120 tofacilitate a fluid-tight seal, as shown. Conductive plate 120 can be onor adjacent to a substrate 130, which is preferably non-conducting(electrically). Substrate 130 can be placed onto a suitable base orsupport surface, e.g., a copper plate (D).

Continuing with the description of FIG. 1, in use for deposition, column(A) can be filled with a plating solution, as described in furtherdetail below. An exemplary plating solution can include a Pt—Ir solutionusing (equal to or about) 0.2 g/L of Sodium hexachloroiridate (III)hydrate, (Na₃IrCl₆·xH₂O) and (equal to or about) 0.186 g/L Sodiumhexachloroplatinate (IV) hexahydrate (Na₂PtCl₆·6H₂O) in 0.1 M nitricacid (HNO₃). An electrical connection can be implemented, e.g.,including toothless copper alligator clip (F), to make electricalcontact between the working electrode lead (WE) and the conductivematerial layer 120. The counter electrode (CE) 108, e.g., made ofplatinum mesh, can be suspended through the top opening of the largercolumn (A). A reference electrode (RE) 106, e.g., made of Ag/AgCl, canbe placed in the smaller-barreled column (B) of the cell 102. Thecross-drilled Luggin capillary (C) can allow for accurate potentialmeasurement without disrupting the field between the working and counterelectrodes 104, 108.

For an exemplary tested embodiment, the cell 102 was made of Teflon. Thelarger chamber (A) contained the Pt counter electrode and the depositionsolution and the smaller chamber contained the reference electrode. Thetwo chambers were connected to each other through a small horizontalsmall via. Gold coated glass slide substrates were the workingelectrodes and were placed on a copper plate with the metalized surfacefacing up and a polymer O-ring was placed on top of the substrateunderneath the larger chamber. The area of working electrode was 0.7cm². The electrodeposition cell was then fixed over the o-ring using asteel spring clamp.

For exemplary tested embodiments, described in further detail below,surface morphology was characterized via scanning electron microscope(SEM) and the chemical compositions of these films were determined usingwavelength dispersive spectroscopy (WDS). The properties of these filmswere evaluated using CV and electrochemical impedance spectroscopy (EIS)and compared against pure Pt, pure Ir and 80-20% Pt—Ir foils. 60-40%Pt—Ir thin film alloys were deposited with thicknesses ranging from 80nm to 500 nm varying as a function of electrodeposition time. with adeposition rate of 16.5 nm/min. Characterizations by SEM and EISrevealed that the surface area of Pt—Ir films increased with increasingfilms thicknesses. The Pt—Ir films were electroplated and evaluated ongold substrate being developed for neural recording and stimulationapplications.

For exemplary tested embodiments, thin films were electrodeposited on1″×3″×0.040″ (25 mm×75 mm×1 mm) glass slide substrates coated with a 50Å chromium adhesion layer covered by a 1000 Å gold layer (EMF Corp). Thesubstrates were chemically cleaned using trichloroethylene, acetone,methanol and finally rinsed with DI water to remove organic impurities.25×25 mm Pt (99.9%), Ir (99.9%) and 80-20% Pt—Ir (99.9%) foils weremechanically polished and electrochemically cleaned by potentialstepping at U=+1.0 V vs. Ag/AgCl and U=−1.0V vs. Ag/AgCl with a durationtime of 30 seconds for each potential, repeated 5 cycles beforeelectrochemical measurements. Pt/Ir films were electrodeposited fromfreshly prepared Pt—Ir solution using 0.2 g/L of Sodiumhexachloroiridate (III) hydrate, (Na₃IrCl₆·xH₂O) and 0.186 g/L Sodiumhexachloroplatinate (IV) hexahydrate (Na₂PtCl₆·6H₂O) in 0.1 M nitricacid (HNO₃). The plating solution was boiled and then cooled to roomtemperature. Before electrodeposition, the Pt—Ir solutions werepre-heated to 62 C. The solutions were agitated using an ultrasonichomogenizer (available from Misonix, Inc.) at a frequency of 20 kHz witha power of 5 W to maintain constant mass transfer duringelectrodeposition and kept the temperature constant. Electrodepositionwas performed in a custom electrochemical cell, FIG. 1, using athree-electrode setup. A Gamry potentiostat was used to controlpotential. Deposition regimens were performed by cycling potential overthe range from U=0.1V to −0.1V vs. Ag/AgCl, at a scan rate of 0.5 V/sfor 300, 600, 1200 or 2400 cycles (equivalent to 4, 8, 16 and 32 minutesof deposition, respectively). The potential was scanned A series ofpotentiodynamic cycles experiments was performed and the depositsobtained at different deposition potentials were analyzed by SEM/EDS,allowing us to determine the threshold electrodepositing potentiallimits corresponding to the maximum amount of Ir to be within +0.1 V to−0.1 V.

Au substrates were weighed before and after each deposition to calculatethin film mass. Film thicknesses were measured twice each byprofilometer (Ambios XP-2 Stylus) and averaged to determine average filmthickness. Total working distance for each scan was 11 mm. 1 mm sectionsthrough the central portion of the film was used from each scan toestimate film thickness.

Pt—Ir thin film surface morphologies were imaged by field emissionscanning electron microscope (ZEISS 1550 VP) with accelerating voltageof 4 kV and a magnification of 100. The chemical compositions of thecontrol foils and electrodeposited Pt—Ir films were characterized byMicroprobe analysis (JXA-8200). Three different spots were analyzed onall samples.

The electrodeposited Pt—Ir thin films, the control foils and Ausubstrate, were electrochemically characterized by cyclic voltammetry(CV) in 0.05 M H₂SO₄ at a scan rate of 50 mV/s over the potential rangeU=−0.3V to 1.2V vs Ag/AgCl. Control samples were mechanically polishedand rinsed with ethanol and DI water to deoxidize and degrease thesamples surfaces prior to characterization. Electrodeposited films werechemically cleaned by ethanol and DI water and then electrochemicallycleaned by applying a step potential at U=+1.32 V and U=−0.32 V vs.Ag/AgCl for 30 seconds each, for 2 cycles in 0.05 M H₂SO₄

Electrochemical impedance spectroscopy (EIS) was performed on the Pt—Irfilms, the control samples and Au substrates. Potentiostaticmeasurements were performed at the open circuit potential (OCP) with a+/−10 mV amplitude ac signal superimposed in 0.05 M H₂SO₄(aq) over thefrequency range 100 KHz to 10 MHz using a Gamry FAS1 potentiostat (GamryInstruments). Experimental data were fitted to a one-time constantequivalent circuit (EC) and the values of the solution resistance(R_(s)), polarization resistance (R_(p)) and capacitance (C) weredetermined using the ANALEIS software COATFIT module.

Thin film deposition cycles recorded at regular time intervals for 32minutes were plotted in FIG. 2 to show cathodic and anodic currentevolution over the deposition period. A plot 200 of the cathodic currentmagnitude at the most negative potential (U=−0.1V vs. Ag/AgCl) showed asteadily increasing current magnitude for most of the depositionprocess, suggesting a steady increase in thin films surface area. SEMmicrographs of electrodeposited thin films were consistent with thisobservation, FIG. 5, showing a progressive increase in surface roughnesswith elapsed time. The growth of the Pt—Ir layers was accompanied by anoverall enlargement of the active area.

FIG. 3 includes FIG. 3A, which shows a plot 300A of the maximum anodiccurrents, and FIG. 3B, which shows a plot 300B of maximum cathodiccurrents as a function of number of cycles. In FIGS. 3A-3B, increases ofthe current in anodic and cathodic directions showed a linear behaviorwith increasing the number of cycles or deposition time. The cathodiccurrents are larger than the anodic currents indicating the reduction ofPt—Ir films with increased active areas.

Pt—Ir deposition rate was characterized via mass change measurement andprofilometry measurement. Profilometry scans were taken over the central5 mm of the electrodeposited Pt—Ir films. FIG. 4, includes FIGS. 4A-4B,which depict two plots of coating properties vs. deposition time, massvs. deposition time 400A and coating thickness vs. deposition time 400B,in accordance with exemplary embodiments of the present disclosure.Based on both profilometry and deposited mass data, Pt—Ir films showedrelatively constant growth rate over the elapsed time period. In thesefigures, mass and thicknesses of the Pt—Ir electroplated films havelinear relationship with deposition time and the deposition rates havemeasured to be 14.76 μg/min and 16.5 nm/min, respectively.

SEM micrographs of the Au substrate and the electrodeposited Pt—Ir filmswhere taken to characterize surface morphology evolution. FIG. 5, whichincludes FIGS. 5A-5E, depicts a set of SEM micrographs 500A-500E, inaccordance with exemplary embodiments of the present disclosure. An Ausubstrate is shown in FIG. 5A and Pt—Ir films are shown in FIGS. 5B-5Ewith four (4), eight (8), 16 and 32 minutes of deposition times,respectively; FIG. 5A shows large the grain sizes of the evaporated Aufilm on top of the glass slide. FIG. 5B corresponds to the Pt—Ir filmgrown for 4 min and presents a more uniform Pt—Ir grain size coating thesurface, in comparison with the grains of the Au substrate in FIG. 5B.FIGS. 5C-5E correspond to eight (8), 16 and 32 minutes of deposition ofPt—Ir films formed on the gold substrate. Visual analysis of themicrographs suggest that the surfaces of the Pt—Ir films increase innodular structure and morphology with increasing deposition time, FIGS.5B-5E. The micrograph for the film obtained by four (4) minutes ofdeposition shows a nanocrystalline structure with size of about 25 nm.In comparison, the thin film deposited for 32 minutes shows averagegrowth in the nanocrystals size has reached the size of 100 nm and thesurfaces of the films have rougher appearance.

Quantitative compositional analysis of 80-20% Pt—Ir foil andelectroplated Pt—Ir films was obtained using an electron microprobe. Thesamples were analyzed by wavelength dispersive spectroscopy(WDS-analysis). Accordingly, the intensities of characteristic X-raylines produced during electron bombardment of a specimen are compared tothat produced from a standard samples using similar instrumentalconditions (accelerating voltage, beam current).

Table I below summarizes the chemical compositions of the 80-20% Pt—Ircontrol sample and electroplated Pt—Ir films, in accordance withexemplary embodiments of the present disclosure. The data in Table Ishow a chemical composition of about 60-40% for 4 minutes and a constantratio of 56-44% for Pt—Ir elements; such data would seem to indicatethat the deposition time after eight (8) minutes, has minimal or almostno effect on the amounts of platinum and iridium in the films.

TABLE 1 Sample Pt (a %) Ir (a %) Pt—Ir (80-20%) 80.3 19.7  4 minutes60.7 39.3  8 minutes 56.2 43.8 16 minutes 56.5 43.5 32 minutes 57.4 42.6

FIG. 6 includes FIGS. 6A-6D with plots 600A-600D, which compare cyclicvoltammagrams for the Au substrate, Pt foil, Ir foil and 80-20 Pt/Irfoils in nitrogen-purged 0.05 M H₂SO₄ (aq) solution. The gold substratevoltammagram showed characteristic features, namely in the anodic sweep,an oxide shoulder and peak spanning from U=0.8V to U=1.2V vs. Ag/AgCl.In the cathodic sweep, the gold oxide reduction peak maximum was locatedat U=0.9V vs. Ag/AgCl and no other features were observed except thehydrogen reduction current beginning near −0.1V vs. Ag/AgCl. In thiscase, the electrode was cycled within a limited potential range and forless than 20 cycles to characterize the metal-solution interaction,therefore iridium activation was limited.

Lastly, the 80-20 Pt/Ir foil voltammagram, FIG. 6D, demonstrated aprofile similar to that of the pure platinum foil, except with lesspronounced hydrogen adsorption and desorption peaks, as would beexpected due to the disruption in the H—Pt lattice binding sites, causedby remnant iridium oxide left on the reduced surface. The consistency ofthe results of these experiments with the literature suggests that theelectrochemical system used was appropriate for characterizing theelectrodeposited films.

FIG. 7 includes FIGS. 7A-7D, which show four plots 700A-700D thatcompare voltammagrams taken from the same four substrates discussedpreviously and compares them with voltammagrams taken from theelectrodeposited thin films. For these measurements, scans ranges wereextended to U=−0.3V to 1.2V vs. Ag/AgCl to capture the entire hydrogenadsorption and desorption peaks for the electrodeposited films.

For pure Pt around −0.12 and −0.22 V, hydrogen under-potentialdeposition, around −0.17 and 0.08 V, hydrogen oxidation and around 0.48V, Pt reduction occurs (FIG. 6 b). For Pt—Ir film with a deposition timeof 4 minutes (FIG. 6 e) the Pt—Ir reduction peak is shifted to around0.35 V and for Pt—Ir films with a deposition times of 8 to 32 minutes(FIG. 6 f-h), the Pt—Ir reduction peak is shifted to around 0.32 V. Itwas found that all electroplated Pt—Ir films (FIG. 6 e-h) did not showthe hydrogen adsorption/desorption peaks which can be attributed to thechanges on the surface structure of Pt due to the formation of IrO₂ inthe oxidation potential range. The number of active sites on the surfaceof Pt can be determined from the hydrogen adsorption and desorption andcan be evaluated from the integrated intensity of these peaks whichsuggests that the active surface area of Pt electrodes can be determinedfrom the adsorption/desorption of hydrogen of Pt electrodes Theseresults suggest that, at these scan rates, the total charge capacitanceof the electrodeposited electrodes is significantly greater than thoseof flat surface area platinum and iridium electrodes.

The Pt/Ir film has a desired composition ratio of Pt to Ir. In exemplaryembodiments, the microelectrode can be cylindrical with a desired lengthand a diameter of between about 0.5 micron to about 200 micron (or anydiameter within the range, inclusive of the end values).

Electrochemical impedance spectroscopy (EIS) data were obtained in 0.05M H₂SO₄ at the open circuit potential (OCP) to assess frequencydependence of charge transfer at the electrode surface. Table 2 showsEIS data obtained.

TABLE 2 Pt—Ir Au Pt (80-20%) Ir 4 min 8 min 16 min 32 min C (F)4.57*10⁻⁵ 9.55*10⁻⁵ 6.3*10⁻⁵ 3.573*10⁻⁴ 1.55*10⁻³ 5.21*10⁻³ 1.11*10⁻²2.01*10⁻² R_(p) 650 815 820 241 78 17 7.8 4.3 (kohm) R_(s) 21.67 22.0822.49 23.06 21.03 21.13 21.28 21.09 (ohm) τ (s) 29.7 77.8 51.7 86.3120.9 88.4 85.8 86.43

The Bode plots in FIG. 7 for all samples and the impedance of theelectroplated Pt—Ir films were observed to drastically decrease byincreasing the deposition time due to increased surface area. Theimpedances for all films compared with the uncoated Au substrate wasobserve to be reduced by more than a factor of 10.

FIG. 8 depicts an equivalent circuit 800 to the electrochemical cell ofFIG. 1. The EIS results of electroplated Pt—Ir films that were testedfollow the one-time constant model with the equivalent circuit shown inFIG. 8, in which the solution resistance R_(s) is in series with aparallel combination of the capacitance of the electrode C andpolarization resistance R_(p).

FIG. 9, includes FIGS. 9A and 9B, which show two Bode plots900(A)-900(B) of experimental and fit data of a Pt—Ir film electroplatedfor 32 minutes, in accordance with a tested embodiment of the presentdisclosure. The plots 900(A)-900(B) seem to indicate that the fit dataare in excellent agreement with the experimental data.

The time constant τ=C*Rp values in Table 2 show similar values for allelectroplated Pt—Ir films indicating that by increasing the C for longerdeposition times, the R_(p) has decreased which proves that theincreased surface area is the only effective factor on the changes ofthe C values.

FIG. 10, including FIGS. 10A-10B, depict plots 1000A-1000B indicating alinear relationship between the C, in (a), and 1/R_(p), in (b), and thedeposition time. The plots 1000A-1000B would appear to indicate that theincrease in the Pt—Ir films thickness occurs in constant rate and isgenerally independent of deposition time.

FIG. 11 depicts a diagram 1100 of an electrochemical potential scaleshowing equilibrium potentials for Pt salts and Ir salts, in accordancewith exemplary embodiments of the present disclosure. The scale ofelectrochemical potentials shows an arbitrary equilibrium potential fora Pt salt (1) and a Ir salt (2). The potential range for deposition can,according to embodiments of the present disclosure, span any of thefollowing ranges: (A) the range may have a negative limit below (1) anda positive limit below (2); the range may have a negative limit below(1) and a positive limit equal to (2); and, the range may have anegative limit below (1) and a positive limit more positive than (2).

The following are details of an exemplary Pt—Ir film depositionprotocol:

For an exemplary tested embodiment, a Pt—Ir electrodeposition bath wasprepared using 0.2 gr/l of Sodium hexachloroiridate (III) hydrate, Ir31.5% min (Na₃IrCl₆·xH₂O) and 0.186 gr/l Sodium hexachloroplatinate (IV)hexahydrate (Na₂PtCl₆·6H₂O) in gr/l of 0.1 M nitric acid (HNO₃). Forelectrodepostion of smooth Pt—Ir thin films, an ultrasonic homogenizerwas used, producing 20 kHz at amplitude of 20 (5 W); where an amplitudeof 20 means 20% of total instrument output for the sonicator. Thesonicator was a Misonix s-4000 Ultrasonic Processor. Theelectrodeposition bath temperature used started around 56 C and thefinishing bath temperature was 62 C. An electrodeposition time of 32minutes was observed to form about 0.45 μm of smooth 60-40% Pt—Ir thinfilm. For the deposition technique, cyclic voltammetry was employedutilizing a scan rate: 500 mV/s.

For the Electrodepostion of rough Pt—Ir thin films, a chemical was addedto the prepared Pt—Ir electrodeposition bath, i.e., 40 g/l of K₂SO₄. Amultrasonic homogenizer was used, with 20 kHz at amplitude of 37 (8 W).The electrodeposition bath temperature started around 56 C and finishedat 75 C. The electrodeposition time was 17 minutes, which was observedto form 0.8 μm of rough 60-40% Pt—Ir film. For the deposition, theapplied potential technique was a potential sweep, with a scan rate 0.2mV/s.

Accordingly, as described above, aspects and embodiments of the presentdisclosure can provide advantages and benefits compared with previoustechniques.

The components, steps, features, benefits and advantages that have beendiscussed are merely illustrative. None of them, nor the discussionsrelating to them, are intended to limit the scope of protection in anyway. Numerous other embodiments are also contemplated. These includeembodiments that have fewer, additional, and/or different components,steps, features, objects, benefits and advantages. These also includeembodiments in which the components and/or steps are arranged and/orordered differently.

In reading the present disclosure, one skilled in the art willappreciate that embodiments of the present disclosure can be implementedin hardware, software, firmware, or any combinations of such, and overone or more networks. Suitable software can include computer-readable ormachine-readable instructions for performing methods and techniques (andportions thereof) of designing and/or controlling the implementation oftailored RF pulse trains. Any suitable software language(machine-dependent or machine-independent) may be utilized. Moreover,embodiments of the present disclosure can be included in or carried byvarious signals, e.g., as transmitted over a wireless RF or IRcommunications link or downloaded from the Internet.

Unless otherwise stated, all measurements, values, ratings, positions,magnitudes, sizes, and other specifications that are set forth in thisspecification, including in the claims that follow, are approximate, notexact. They are intended to have a reasonable range that is consistentwith the functions to which they relate and with what is customary inthe art to which they pertain.

All articles, patents, patent applications, and other publications whichhave been cited in this disclosure are hereby incorporated herein byreference.

The phrase “means for” when used in a claim is intended to and should beinterpreted to embrace the corresponding structures and materials thathave been described and their equivalents. Similarly, the phrase “stepfor” when used in a claim embraces the corresponding acts that have beendescribed and their equivalents. The absence of these phrases means thatthe claim is not intended to and should not be interpreted to be limitedto any of the corresponding structures, materials, or acts or to theirequivalents.

Nothing that has been stated or illustrated is intended or should beinterpreted to cause a dedication of any component, step, feature,benefit, advantage, or equivalent to the public, regardless of whetherit is recited in the claims.

The scope of protection is limited solely by the claims that now follow.That scope is intended and should be interpreted to be as broad as isconsistent with the ordinary meaning of the language that is used in theclaims when interpreted in light of this specification and theprosecution history that follows and to encompass all structural andfunctional equivalents.

1. A method of depositing a platinum-iridium alloy, the methodcomprising: causing contact between a metal base and an electrolytesolution for electrodeposition, wherein the electrolyte solution isnon-cytotoxic and comprises platinum and iridium; causing contactbetween two or more electrodes and the electrolyte solution, wherein theelectrodes are configured to apply an electric potential to theelectrolyte solution; causing electrical contact between at least one ofthe two or more electrodes and the metal base; and applying an electricpotential to two or more of the electrodes in the electrolyte solutionin an amount sufficient cause deposition of Pt—Ir on the metal base. 2.The method of claim 1, wherein the electrolyte solution contains adesired concentration of a platinum salt and a desired composition of aniridium salt, and wherein the resultant solution provides a thin film ofdesired composition of Pt and Ir after deposition.
 3. The method ofclaim 1, further comprising heating the electrolyte solution to improvestability of salt in solution.
 4. The method of claim 1, whereinproviding an electrolyte solution comprises providing an electrolytesolution that is lead free.
 5. The method of claim 1, wherein providingan electrolyte solution comprises providing an electrolyte solution thatcontains no cytotoxic constituents.
 6. The method of claim 1, whereinproviding an electrolyte solution comprises providing an electrolytesolution that has a near neutral pH between about 6 to about 8 pH. 7.The method of claim 1, wherein providing an electrolyte solutioncomprises providing an electrolyte solution that has a pH from about 1.5to 2.5.
 8. The method of claim 1, wherein applying an electric potentialcomprises potential cycling.
 9. The method of claim 8, wherein applyingan electric potential comprises using a single cycle.
 10. The method ofclaim 1, wherein applying an electric potential comprises potentialpulsing.
 11. The method of claim 1, wherein applying an electricpotential comprises potential ramping.
 12. The method of claim 1,wherein applying an electric potential comprises potential stepping to alevel more negative to the equilibrium potentials for reduction of boththe Pt and Ir salts used for electroplating.
 13. The method of claim 1,wherein applying an electric potential produces an electrodeposited thinfilm of desired electrochemical impedance.
 14. The method of claim 1,wherein applying an electric potential produces an electrodeposited thinfilm of desired surface roughness/unit surface area.
 15. The method ofclaim 14, wherein applying an electric potential produces anelectrodeposited thin film of desired porosity or lack thereof.
 16. Themethod of claim 1, wherein the composition of the Pt—Ir alloy is about80% Pt and 20% Ir.
 17. The method of claim 1, wherein the composition ofthe Pt—Ir alloy is about 60% Pt and 40% Ir.
 18. The method of claim 1,wherein the composition of the Pt—Ir alloy is about 95% Pt and 5% Ir.19. The method of claim 1, wherein the electrolyte solution comprisessodium hexachloroiridate (III) hydrate (Na₃IrCl₆·xH₂O) and sodiumhexachloroplatinate (IV) hexahydrate (Na₂PtCl₆·6H₂O).
 21. The method ofclaim 19, wherein the electrolyte solution comprises nitric acid (HNO₃).22. The method of claim 19, wherein the electrolyte solution comprisesnitric acid (HNO₃) at a concentration of about 0.1 M.
 23. The method ofclaim 19, wherein the electrolyte solution comprises sodiumhexachloroiridate (III) hydrate (Na₃IrCl₆·xH₂O) at a concentration ofabout 0.2 g/L.
 24. The method of claim 19, wherein the electrolytesolution comprises sodium hexachloroplatinate (IV) hexahydrate(Na₂PtCl₆·6H₂O) at a concentration of about 0.186 g/L.
 25. The method ofclaim 19, further comprising adding a salt for increasing surfaceroughness.
 26. The method of claim 25, wherein the salt comprisespotassium sulfate (K₂SO₄).
 27. The method of claim 1, wherein thecomposition of the Pt—Ir alloy is in the range from about 98% Pt and 2%Ir to about 60% Pt and about 40% Ir.
 28. The method of claim 1, whereinthe composition of the Pt—Ir alloy is in the range from about 90% Pt and10% Ir to about 60% Pt and about 40% Ir.
 29. The method of claim 1,wherein the composition of the Pt—Ir alloy is in the range from about98% Pt and 2% Ir to about 90% Pt and about 10% Ir.
 30. A Pt/Irmicroelectrode comprising: a metal base of a selected metal composition;a Pt/Ir film disposed on the metal base, wherein the Pt/Ir film has adesired composition ratio of Pt to Ir.
 31. The microelectrode of claim30, wherein the selected composition is about 80% Pt and 20% Ir.
 32. Themicroelectrode of claim 30, wherein the selected composition is about60% Pt and 40% Ir.
 33. The microelectrode of claim 30, wherein theselected composition is about 95% Pt and 5% Ir.
 34. The microelectrodeof claim 30, wherein the selected composition is in the range from about98% Pt and 2% Ir to about 60% Pt and about 40% Ir.
 35. Themicroelectrode of claim 30, wherein the selected composition is in therange from about 90% Pt and 10% Ir to about 60% Pt and about 40% Ir. 36.The microelectrode of claim 30, wherein the selected is in the rangefrom about 98% Pt and 2% Ir to about 90% Pt and about 10% Ir.
 37. Themicroelectrode of claim 30, wherein the Pt/Ir film has a desired surfaceroughness.
 38. The microelectrode of claim 30, wherein the Pt/Ir filmhas a desired electrochemical impedance.
 39. The microelectrode of claim30, wherein the Pt/Ir film has desired mechanical properties.
 40. Themicroelectrode of claim 30, wherein the metal base comprises gold. 41.The microelectrode of claim 30, wherein the metal base comprisesplatinum.
 42. The microelectrode of claim 30, wherein the metal base iscylindrical.